This application relates generally to gas turbine engine rotor blades and, more particularly, to methods and apparatus for reducing tip spillage across a rotor blade tip.
Gas turbine engine rotor blades typically include airfoils having leading and trailing edges, a pressure side, and a suction side. The pressure and suction sides connect at the airfoil leading and trailing edges, and span radially between the airfoil root and the tip. An inner flowpath is defined at least partially by the airfoil root, and an outer flowpath is defined at least partially by a stationary casing. More specifically, the stationary casing is positioned radially outwardly from the airfoil tips such that a gap is defined between the shroud and the airfoil tips.
For example, such blades are used in at least some known compressors, and during compressor assembly, the gap defined between the shroud and airfoil tips is sized to permit differential growth of the rotating airfoil tips and the stationary casing throughout compressor operation. More specifically, during engine operation, the gap may increase due to airfoil tip erosion or manuever loading. Over time, continued operation of the compressor with the increased gap may cause tip to casing flow interference. Furthermore, as a result of the inherent pressure differential created on opposite sides of the operating blade, an increased gap may permit air to undesirably flow across the airfoil tip from the pressure side of the airfoil to the suction side of the airfoil. Such undesirable air flow is known as parasitic flow or tip spillage and may adversely affect the operating efficiency of the compressor.
To facilitate reducing tip spillage, at least some known compressor rotating blades include a rotating tip shroud that is attached to the airfoil tip to facilitate minimizing the radial gap between the blade and the casing. Although the tip shroud also facilitates reducing tip spillage, the configuration may also introduce complex interfaces between adjacent airfoil tips, and increases an overall weight of the rotor structure. At least some other known compressor rotor blades employ winglets attached to the airfoil tip to facilitate inhibiting tip spillage. However, known winglet designs are limited in use because of the design challenges presented in attaching the winglets to the airfoils and in close proximity to the stationary case.